Need advice on what legal action to take if pet was shot

My dog was a lab she would go out around the culdesac and play. Everyone knew her I had her for over ten months. I let her out last Thursday and my neighbor who is a police who was walking his dog (terrier) shot her. I did not see but he admitted to me that he saw the dog coming at him so he shot her. She always runs up to his dog when his father carried it around, because she is curious and want to play. I want to know what legal action I can take against this man. He is a police officer. I had to put her to sleep because I was told not survival may not be sure and it cost too much.